Zinc plating brightener



United States Patent 3,112,251 ZINC PLATIN G BRIGHTENER Isaac L. Newell, 209 Brimfield Road, Wethersfield, Conn., and William F. Houlihan, 15 Wellington St., Springfield, Mass.

No Drawing. Filed Aug. 17, 1961, Ser. No. 131,980 13 Claims. (Cl. 20455) This invention relates to zinc cyanide plating baths and more particularly to improvements in zinc plating baths to improve the brightness and color of the metals precipitated from such baths.

While a great many additives have been suggested for improving the brightness of electro deposits from zinc cyanide plating baths, these have usually been composed of complex mixtures of materials which have been more or less non-uniform, thereby leading to unpredictable and haphazard results.

It is one object of this invention to provide an addition agent'for zinc cyanide plating baths which Will be uniform in composition and which will impart a uniform brightness to the metal deposited from such baths.

A further object of this invention is to broaden the current density range within which bright electro deposits of zinc can be obtained.

Still another object of this invention is to provide good brightness and color of deposits from such baths in spite of the presence of significant amounts of impurities therein.

Other objects of the present invention Will in part be obvious and will in part appear hereinafter.

These and other objects are achieved by adding, in

combination, certain monoor poly-saccharides and aldehyde bisulfites to the plating baths.

As examples of the monosaccharides are the 5 carbon atom molecules such as xylose:

Examples of the 6 carbon monosaccharides are mannose:

OH OH Examples of the polysaccharides are lactose:

and sucrose:

HO t) CHzOH Typical of aldehyde bisulfites suitable for use may be mentioned the bisulfites of anisic aldehyde, benzaldehyde, o-ethoxy benzaldehyde, salicylaldehyde, furfuraldehyde, and mixtures of the foregoing. Other suitable aldehyde bisulfites of the cyclic or aromatic aldehyde type will readily suggest themselves to those skilled in the art.

The brighteners described herein may be used with any suitable commercial zinc cyanide plating bath. Such baths generally comprise alkaline aqueous solutions of zinc and cyanide ions, and are prepared, for example, by dissolving zinc cyanide in an aqueous solution of an alkali metal hydroxide, e.g., sodium hydroxide, potassium hydroxide, lithium hydroxide, and so forth. Such solu tions also generally comprise a water-soluble alkali metal cyanide salt, e.g., sodium cyanide, potassium cyanide, lithium cyanide, and the like. Also, if desired, zinc oxide, rather than zinc cyanide, may be dissolved in an aqueous solution of alkali metal hydroxide and Water-soluble cyanide salts.

The weight ratio of alkali cyanide to zinc in such solutions is quite important. 'In general the weight ratio of alkali cyanide to zinc may vary between about 2.0 and 3.5 to 1. In use the plating bath should be analyzed periodically to insure the proper ratio of alkali metal cyanide to zinc.

Alkaline Zinc cyanide baths are well known, and no attempt will be made here to describe in detail all of the possible features thereof, inasmuch as such details will be obvious to those skilled in the art.

Zinc cyanide plating baths having the following compositions are especially suitable for use in the present invention and are preferred:

Zinc metal 3.5 to 6.0 oz./ gal. Total sodium cyanide 11.0 to 18.0 oz./ gal. Sodium hydroxide (flake) 8.0 to 13.0 oz./gail. Water To make one gallon. Ratio NaCN/Zn 2.5 to 32:1.

The amount of monoor poly-saocharides in the bath may vary between about 0.05 and 10 ounces/ gallon, and the amount of aldehyde bisulfite may vary between about 0.1 and 25 ounces/gallon. Although good results are generally obtained by using the amounts of aldehyde bisulfite and monoor poly-saccharides indicated, improvements may be obtained by regulating the relative proportion of aldehyde bisulfite and monoor poly-sacchan'des added to the bath. For best results, the weight ratio of aldehyde bisulfite to monoor poly-saccharides should be at least 1 to 1 or between about 1 and 6 to 1 or higher. More generally, this ratio may vary between about 1 and 100, and even higher.

Regular additions of these brighteners to the plating baths prolong the life of the baths, so that bright metal plating may be achieved in spite of the presence of significant amounts of heavy metal impurities therein.

If the build-up of heavy metal impurities becomes too great, in addition to the brighteners, zinc dust may be sprinkled over the surface of the bath. The amount of zinc dust may vary between about 0.5 and 4 pounds, and usually between about 1 and 2 pounds of zinc dust per 100 gallons of solution. Following addition of the Zinc dust, the solution may be allowed to settle for a few hours or overnight, and may then be filtered or decanted to remove the zinc dust.

The following illustrates one method of preparing zinc cyanide baths suitable for use in carrying out the invention:

About one-half of the water requirement is charged to a make-up tank and sodium hydroxide dissolved therein. The sodium cyanide is then charged with stirring. In a separate container, zinc cyanide is added to sufficient water to form a thick slurry. This slurry is then added to the make-up tank with stirring.

The volume :of the solution is then brought up to proper operating level with cold water and the indicated amount of monoor polysaccharides and aldehyde bisulfite added thereto.

The monoor poly-saccharides and aldehyde bisulfites may be added to the bath at any stage. Preferably, however, they' are added after the bath has been brought up to proper volume. These materials may be added as a dry solid, or as an aqueous solution. When added as an aqueous solution, care should be taken to insure the addition of the proper amounts.

The use temperature of the plating baths may vary between about 60 and 100 F., and is preferably between about 80 and 85 F. The current density range may vary between about 1 and 100 amperes per square foot.

The nature of the present invention will be clear from the following examples, which although specific, are not intended to limit the invention in any way, except as such limitations appear in the claims.

A zinc cyanide bath having the following composition is prepared:

Oz./gal. Zinc metal 4.5 Total sodium cyanide 12.3 Caustic soda 10.4

Water to make 1 gallon.

Equal parts of the aldehyde bisulfite and saccharide indicated in the table are mixed, and then the mixture is added to the bath at a rate of 0.50 oz./ gal.

The resulting bath is added to the zinc plating cell designed to give a range of current densities from low to high across the cathode. This is accomplished by having the cathode plate fixed at an angle to the anode.

Electroplating is carried out at a temperature of 80 to 85 F. for 3 minutes at current density range of 1 to 100 amperes per square foot.

As a control is used the identical bath with the exception that no brightener is added.

A. The following table gives the results of the runs:

Aldehyde Bright Cur- Haze Cur- Run Saccharide Bisulfite rent Density rent Density Range ASF Range AS 1* l Mannose" Anisic 10-20 very 20-100 light bright. haze; 3.0-10

light haze.

2 Mann0se Benzaldehydc. 10-30 201- light ram.

3 Xylose O-Ethoxy..." Slight increase light haze Benzaldein bright- 5-100. hyde. ness 5-100.

4 .do Salieylade- 35-10 40-100 light hyde. haze; 5-35 medium haze.

5 Lactose-.. Furfumlde- 10-25 very 25-100 light hyde. bright. haze.

0 Control... No addition None Heavy haze agent. 0.

In using the present invention in commercial plating baths, sulfide additions commonly used to control heavy metals have no effect on the brightness. Moreover, surface active agents such as alkyl sulfonates may be used to control surface tension without adverse effects.

The invention in its broader aspects is not limited to the specific compositions and procedures shown and described but departures may be made therefrom, within the scope of the accompanying claims, without departing from the principles of the invention and without sacrificing its chief advantages.

1. A composition of matter for improving the brightness of zinc deposits from alkaline zinc plating baths which consists essentially of a saccharide which is a member selected from the group consisting of xylose, arabinose, mannose, glucose, fructose, galactose, lactose and sucrose, and an aldehyde bisulfite selected from the group consisting of bisulfites of cyclic and aromatic aldehydes, the weight ratio of aldehyde bisulfite to the saccharide being between about 1 and 100 to 1.

2. The composition of claim 1 wherein the weight ratio of aldehyde bisulfite to saccharide is between 1 and 6:1.

3. A method for improving the brightness of zinc deposits from alkaline zinc cyanide plating baths over the current density range of 1 to 100 amperes per square feet which comprises adding to the Zinc cyanide plating baths a brightener consisting essentially of a saccharide which is a member selected from the group consisting of xylose, arabinose, mannose, glucose, fructose, galactose, lactose, and sucrose, and an aldehyde bisulfite taken from the group consisting of bisulfite of anisicaldehyde, benzaldehyde, o-ethoxy benzaldehyde, salicylaldehyde, and furfuraldehyde, the amount of the saccharide being between about 0.05 and 10 ounces per gallon, and the amount of aldehyde bisulfite being between about 0.1 and 25 ounces per gallon.

4. A composition of matter for improving the brightness of zinc deposits from alkaline zinc plating baths which consists essentially of a saccharide which is a member selected from the group consisting of xylose, arabinose, mannose, glucose, fructose, galactose, lactose, and sucrose, and an aldehyde bisulfite taken from the group consisting of bisulfite of anisicaldehyde, benzaldehyde, oethoxy benzaldehyde, salicylaldehyde, and furfuraldehyde, the weight ratio of aldehyde bisulfite to the saccharide being between about 1 and 100 to 1.

5. An alkaline aqueous cyanide bath electrolyte consisting essentially of, in solution, 3.5 to 6.0 ounces per gallon of zinc metal, 11.0 to 18.0 ounces per gallon of sodium cyanide, 8.0 to 13.0 ounces per gallon of an alkali metal hydroxide, 0.05 to 10 ounces per gallon of a saccharide selected from the group consisting of xylose, arabinose, mannose, glucose, fructose, galactose, lactose, and sucrose, and from about 0.1 to 25 ounces per gallon of an aldehyde bisulfite selected from the group consisting of anisicaldehyde, benzaldehyde, o-ethoxy benzaldehyde, salicylaldehyde, and furfuraldehyde.

6. An alkaline zinc cyanide electrolyte having a ratio of alkali metal cyanidezZn of 2.5 to 3.5:1 and containing a brightener consisting essentially of a member selected from the group consisting of xylose, arabinose, mannose, glucose, fructose, galactose, lactose and sucrose, and an aldehyde bisulfite selected from the group consisting of bisulfites of cyclic and aromatic aldehydes, the amount of the saccharide being between about 0.05 and ounces per gallon, and the amount of aldehyde bisulfite being between about 0.1 and 25 ounces per gallon.

7. The composition of matter of claim 4 wherein the weight ratio of aldehyde bisulfite to the saccharide is between about 1 and 6 to 1.

8. The alkaline zinc cyanide electrolyte of claim 6 wherein the weight ratio of aldehyde bisulfite to the saccharide is between about 1 and 6 to 1.

9. The method of claim 3 wherein the weight ratio of the aldehyde bisulfite to the saccharide is at least 1 to 1.

10. In a process for the electrodeposition of zinc, the improvement which comprises depositing zinc from a cyanide zinc plating bath containing between about 0.05 and 10 ounces per gallon of a saccharide which is a member selected from the group consisting of Xylose, arabinose, mannose, glucose, fructose, galactose, lactose and sucrose, and between about 0.1 and 25 ounces per gallon of an aldehyde bisulfite selected from the group consisting of bisulfites of cyclic and aromatic aldehydes, the weight ratio of the aldehyde bisulfite to the saccharide being between about 1 and 100 to 1.

11. The method of claim 10 wherein the weight ratio of aldehyde bisulfite to the saccharide is between about 1 and 6 to 1.

12. An alkaline Zinc cyanide electrolyte containing a brightener which consists essentially of saccharides which are members selected from the group consisting of Xylose, arabinose, mannose, glucose, galactose, lactose and sucrose, and an aldehyde bisulfite which is a member selected from the group consisting of bisulfite of anisic aldehyde, benzaldehyde, o-ethoXy benzaldehyde, salicylaldehyde and furfuraldehyde, the amount of saccharide being between about 0.05 and 10 ounces per gallon, and the amount of aldehyde bisulfite being between about 0.1 and 25 ounces per gallon, the weight ratio of aldehyde bisulfite to the saccharide being between about 1 and 100.

13. An alkaline Zinc cyanide electrolyte having a ratio of alkaline metal cyanide to Zinc of between about 2.5 and 3.5 to 1, and containing a brightener consisting essentially of saccharide which is a member selected from the group consisting of xylose, arabinose, mannose, glucose, fructose, galactose, lactose, and sucrose, and an aldehyde bisulfite which is a member selected from the group consisting of bisultites of anisic aldehyde, benzaldehyde, oethoxy benzaldehyde, salicylaldehyde, and furfuraldehyde, the amount of the saccharide being between about 0.05 and 10 ounces per gallon, and the amount of the aldehyde bisulfite being between about 0.1 and 25 ounces per gallon, the weight ratio of aldehyde bisulfite to saccharide being between about 1 and 100.

References Cited in the file of this patent UNITED STATES PATENTS 694,658 Meurant Mar. 4, 1902 2,390,511 Chester Dec. 11, 1935 2,740,754 Hofiman Apr. 3, 1956 OTHER REFERENCES Wernlund: Journal of the Elec. Soc., vol. 40, 1921; pages 257-285. (Copy in Div. 56.)

Karrer: Organic Chemistry, 1946, Elsevier Publ. Co.; pages 250, 310. (Copy in Div. 43.)

Hackhs Chemical Dictionary, Blakiston Co., 1944, page 476. (Copy in Div. 56.) Y 

1. A COMPOSITION OF MATTER FOR IMPROVING THE BRIGHTNESS OF ZINC DEPOSITS FROM ALKALINE ZINC PLATING BATHS WHICH CONSISTS ESSENTIALLY OF A SACCHARIDE WHICH IS A MEMBER SELECTED FROM THE GROUP CONSISTING OF XYLOSE, ARABINOSE, MANNOSE, GLUCOSE, FRUCTOSE, GALACTOSE, LACTOSE AND SUCROSE, AND AN ALDEHYDE BISULFITE SELECTED FROM THE GROUP CONSISTING OF BISULFITES OF CYCLIC AND AROMATIC ALDEHYDES, THE WEIGHT RATIO OF ALDEHYDE BISULFITE TO THE SACCHARIDE BEING BETWEEN ABOUT 1 AND 100 TO
 1. 